1. Field of the Invention
The present invention relates to optical magnetic-field sensors mainly used for forming a fault point-detecting system in electric power supply line networks, electric power distribution line networks, and transformer stations.
2. Related Art Statement
Recently, in order to automatically detect fault points in electric power supply systems, optical magnetic-field sensors using optical single crystals, for example, BSO, etc., have been used wherein a light beam emitted from a transmitter is transmitted through a magnetooptical element and detected by a receiver. If an electric current thereof is rapidly changed by short-circuiting or grounding, a magnitude of the electric field generated around the power supply line is changed thereby changing a polarized plane of the light beam transmitted through the magnetooptical element, so that the change is detected to judge an occurrence of a fault in the power supply line.
In optical magnetic-field sensors, a polarizer, a magnetooptical element and an analyzer are accommodated in a housing case with their optical axes aligned to each other. However, spaces between the magnetooptical element and polarizer or the analyzer result in loss of light transmitting through the optical magnetic-field sensor. Thus, heretofore, the distance between the transmitter and a detected fault point and the distance between the receiver and the detected fault point were limited.
The applicants disclosed in their Japanese patent application Laid-open No. 63-047,723 a technique of inserting an intermediate body, such as glass, etc. in the space between the magnetooptical element and the optical parts and adhering them to each other to mitigate thermal expansion thereof. In this case also, losses of the amount of the light beam at the interfaces between the intermediate body and the magnetooptical element or the optical parts were one of major problems. Large influence of temperature change over modulation rate was also a major problem.
Meanwhile, Japanese patent application Laid-open No. 63-210,911 disclosed a technique of fixing the magnetooptical element and the optical parts to a substrate via an intermediate body. However, in this case there arise problems in that a large amount of the light beam is lost, and the surface of the magnetooptical element adhered to the intermediate body tends to peel off due to thermal stress generated by temperature change a transformer station, etc, so that the magnetooptical element is displaced. Therefore, the technique has problems with respect to long term durability.